Differences between Blatta orientalis and Periplanata americana are
Blatta orientalis :
Brownish-black to black coloured.
20-25 mm, smaller in size.
Less capable of flying.
Forewings are vestigial. Hindwings are absent
.Ootheca is black-coloured
Periplanata americana :
35-40 mm, larger in size.
Good capacity of flying.
In both sexes, both pairs of wings are well developed.
Ootheca is grey-coloured.